Jerrys88

Also trying to keep it simple:

Fib - my suggestion for learning to use your gears:

Go for a ride that includes some hills. Concentrate on picking a pedaling speed and maintaining it, no matter if you're riding on flat terrain or going up or down hill.

The speed at which you're pedaling is called "cadence." If you are a musician and have a metronome, set it somewhere between 80 and 90 and stick it in your pocket. If you don't have a metronome, you can download a metronome app on your smartphone. Start out by picking a gear at which you can pedal one full revolution per beat you hear with a comfortable resistance - not too hard, not to easy (don't be fooled - one full revolution will feel like TWO because it means 1) one foot forward 2) the other foot forward.)

Switching gears has most to do with keeping a steady cadence no matter what the terrain is. In order to keep your cadence steady, you'll find that when you're going up hill, you'll need to shift down to an easier gear, and shift back up for flat or downhill terrain. The clue for when you need to shift will be if pedaling resistance gets too hard to keep up with the beat, or the resistance becomes so easy that you find yourself pedaling faster than the beat.

Just for simplicity, think of your FRONT three chainrings as:

Big Ring = Down Big Hill
Middle Ring = Most Riding
Small Ring = Up Big Hill

Also, for simplicity, since you state that where you live there are no big hills, for the cadence practice I suggested, put the chain on the front middle ring and keep it there. Do all your shifting in the back.

Re noise you heard, yes - you probably cross-chained:

Front Small Ring + Back Small Sprocket
or
Front Large Ring + Back Large Sprocket

Either one will put your chain at a severe angle and will likely make noise. Try to avoid them.